Oil palms (Elaeis guineensis, Elaeis oleifera, or a cross thereof) are palms that are grown to produce oil. Oil palms grow up to 20 meters tall. Their fruit is reddish in color and about the size of a plum. The fruits grow in large bunches which grow around the palm. The time from pollination of the flowers to maturation of the fruit is about five to six months. Oil palms produce bunches year-round and the fruits are harvested as they reach maturity.
The oil palm's fruit consists of a fleshy outer layer that surrounds a palm kernel. Oil is extracted from the pulp of the fleshy outer layer and from the kernel. Oil palm is an important crop for vegetable oil production and is grown on about 15 million hectares worldwide (UNEP Global Environmental Alert Service, December 2011). The demand for palm oil is expected to double by 2020. To meet the increasing demand for palm oil and improve efficiency, agronomic methods such as tree spacing, increased planting, fertilization, and irrigation as well as genetic improvement have been developed to optimize oil production (Corley, R. H. V. and P. B. Tinker, 2003, The Oil Palm, 4th edition, New York, John Wiley and Sons, 590 pp). There is still a need, however, for methods to increase production of currently planted oil palms. There is also still a need to increase oil production in order to maximize the oil production of the plants produced through genetic improvement. Further, there is a need to increase oil production of the palms managed by spacing, increased planting, fertilization, and irrigation.
Ethylene is a two carbon gaseous hydrocarbon molecule that acts as a regulator of plant growth and development. Ethylene plays important roles in many physiological processes through the lifecycle of plants including the promotion of germination, reduction of early plant growth, increase in male flower number, abscission of flowers and fruit, and promotion of ripening (Abeles, F. A., et. al., 1992, P. W. Morgan and M. E. Saltveit, Ethylene in Plant Biology, 2nd edition, 414 p., Academic Press, New York, 1992).
The effect of ethylene on the oil content of oil palm fruit is not well understood, however, the available literature suggests that application of ethylene increases oil content. For example, Chan, et al. (1972, Ann. Appl. Biol. 71:243-249) showed that preharvest application of the ethylene-releasing agent ethephon (2-chloroethyl phosphonic acid) to attached bunches of oil palm fruit increased oil content by 7%. Tranbarger, et al. (2011, Plant Physiol. 156:564-584) found concomitant increase in preharvest oil content and the ethylene level generated endogenously in the oil palm fruit. These reports suggest a relationship between increased ethylene levels and increased palm oil content.
Despite showing promise as a way to increase oil content, ethylene has numerous negative effects on plants which are well known in plant physiology. For example, ethylene promotes abscission of fruits and flowers which would decrease yield and yield potential. In fruit trees and bulbs, ethylene can cause the physiological disease gummosis. Gummosis is a generalized disorder of trees in which polysaccharide gum is overproduced, exuded, and deposited on the bark. Gummosis affects water relations, promotes disease, is attractive to wood-boring insects, causes shoot death, and leads to early tree decline. Based on these effects, application (particularly repeated application) of ethylene may not provide an overall benefit in oil palm.
In addition, few studies have examined the effect of ethylene antagonists on oil palm and of those studies, ethylene antagonists were applied after harvest. For example, Henderson and Osborne (1994) showed that a postharvest application of the ethylene biosynthesis inhibitor aminooxyacetic acid (AOA) delayed or suppressed abscission of oil palm fruit in detached bunches (J. Exper. Bot. 45:943-951). Based on this study and others, it is unclear whether ethylene antagonists will be beneficial as a pre-harvest treatment.
Accordingly, there is a need for practical methods to increase the amount of oil that oil palm trees produce. These methods should produce more oil while not harming the oil palm and should be easy to apply to the fruit or oil palm.